1. Field of the Invention
The present invention relates to a structure of thin film type common mode noise filter, and in particular, to a thin film coil formed on an insulation substrate with a less expensive cost yet is capable of eliminating high frequency common mode noise, and also to its fabrication method.
2. Description of the Related Art
In U.S. Pat. No. 7,145,427B2, there disclosed “Coil Component and Method of manufacturing the Same” in which a common mode noise filtering element forms a coil component on a magnetic substrate and then a cavity is caved by etching process on part of the substrate where no coil component occupies, after that the surface thereof is flattened by filling with the magnetic powder mixed with colloidal substance, and followed by the gluing process to bond with another magnetic material thereby completing the fabrication.
In the other U.S. Pat. No. 6,356,181 B1 and 6,618,929 B2, a layered common mode noise filter is disclosed. In both cases, a coil structure is established on a magnetic substrate and then covered by a magnetic substrate. The kernel of both cases lies in that a special wiring skill is employed for the coil to lessen the impedance of the differential signals.
However, all the aforementioned fabrication methods have the same shortcomings of complexity, time wasting and high cost in its fabrication. When using a magnetic material as the substrate, the ability to filter the common mode noise can not exceed −20 dB, and the manufacturing cost of the common mode noise filter never comes down under such situations.
The inventor of the present invention herein provides a common mode noise filter which is simply constructed and can be fabricated with a low cost, yet having common mode noise filtering characteristic of above −30 dB, and also the fabrication method thereof is to be elucidated.